Effects of live-release tournament regulation changes for an Iowa Largemouth Bass population

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Maahs, Brandon
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Michael J Weber
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Natural Resource Ecology and Management
The Department of Natural Resource Ecology and Management is dedicated to the understanding, effective management, and sustainable use of our renewable natural resources through the land-grant missions of teaching, research, and extension.
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During the early 1960s Largemouth Bass (Micropterus salmoides; hereafter referred to as bass) populations were being overharvested due to harvest-oriented tournaments and recreational angling. As competitive tournaments continued to grow in popularity, catch-and-release angling was promoted through live-release tournaments in response to overharvest concerns for bass populations. The use of live-release tournaments successfully created a paradigm shift in bass anglers’ mindset and by 1980 most bass tournaments were live-release. However, with the use of live-release tournaments, anglers were challenged to keep bass alive until release after the tournament’s weigh-in. Despite anglers’ best efforts, confinement and weigh-in stressors still resulted in bass initial and delayed tournament mortality. While many environmental, confinement, handling, and angler related factors affect tournament mortality, how the number of bass in a live-well affects tournament mortality has received little attention. Additionally, evaluating methods to reduce tournament mortality is critical if tournament mortality becomes an issue, especially in areas like Iowa where tournaments are focused on a few popular bass fisheries. Length and bag limits are commonly used to manage harvest in recreational fisheries, but it is unclear how effective these harvest regulations are at managing number of bass weighed in and the associated mortality of bass at live-release bass tournaments. In 2018, the Iowa legislature passed new bass tournament regulations increasing the bag limit from three bass to five bass and reducing the minimum length limit from >381 mm to no minimum length limit. The liberalized tournament regulations provided a unique opportunity to evaluate current tournament management techniques. Thus, the objectives of this study were to: 1) evaluate the relative effect number of bass in a live-well has on post-release tournament survival compared to environmental characteristics and bass length and 2) identify effects of tournament regulations relative to environmental characteristics and angler factors on bass tournament capture probability and how harvest regulations could be used to reduce delayed tournament mortality. To meet these objectives, a mark-recapture study was conducted on Brushy Creek Lake, Iowa from 2015-2019. Bass were collected and tagged during all tournaments (n = 205) and monthly electrofishing events. To evaluate my first objective, a Cormack-Jolly-Seber model in Program MARK was used to estimate the duration of reduced post-release tournament survival (0 – 7 day) and the effect number of bass in a live-well (1 – 15 bass) has on post-release tournament survival compared to environmental and bass length covariates. Models indicate reduced post-release survival occurs over a 3-day period with water temperature having the greatest effect on post-release survival. Survival was also negatively correlated with number of bass in a live-well; however, reduced survival due to crowded live-wells likely has minimal population effects due to the infrequency of ten or more bass in a live-well. A before-after-control-impact design was then used to evaluate if tournament anglers during the post-regulation change period (2018-2019) weighed in more bass per angler per tournament hour than anglers’ pre-tournament regulation change (2015-2017). Tournament anglers weighed in an average of 0.26 bass per angler per tournament hour and anglers did not weigh-in more bass post-regulation change. Finally, a live capture multistate model in Program MARK was used to assess the relative effects of tournament regulations, angler effort, and environmental characteristics on bass capture probability. Environmental characteristics (water temperature and wind speed) were more supported than length and bag limits in describing tournament angler bass capture probability. If bag limits were reduced to a one bass limit, tournament mortality could be reduced by 60%. However, bass capture probability was highest in spring when tournament mortality was low whereas capture probability was low during periods of high tournament mortality, resulting in simulated length and bag limits having little effect on tournament mortality. Thus, if tournament mortality becomes an issue, other management methods that do not rely on bass catchability may provide a more reliable option to reduce number of bass weighed in and the associated tournament mortality. The results of this study help broaden the understanding of confinement related stress for tournament captured bass and provide insight on how effective current management techniques are at managing live-release bass tournaments.

Tue Dec 01 00:00:00 UTC 2020